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Feb 12, 2021

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Kubebuilder

Kubebuilder is a framework for building Kubernetes APIs using custom resource definitions (CRDs).

Similar to web development frameworks such as Ruby on Rails and SpringBoot, Kubebuilder increases velocity and reduces the complexity managed by developers for rapidly building and publishing Kubernetes APIs in Go. It builds on top of the canonical techniques used to build the core Kubernetes APIs to provide simple abstractions that reduce boilerplate and toil.

Kubebuilder does not exist as an example to copy-paste, but instead provides powerful libraries and tools to simplify building and publishing Kubernetes APIs from scratch. It provides a plugin architecture allowing users to take advantage of optional helpers and features. To learn more about this see the Plugin section.

Kubebuilder is developed on top of the controller-runtime and controller-tools libraries.

Kubebuilder is also a framework

Kubebuilder is extensible and can be used as a library in other projects. Operator-SDK is a good example of a project that uses Kubebuilder as a library. Operator-SDK uses the plugin feature to include non-Go operators e.g. operator-sdk's Ansible and Helm-based language Operators.

To learn more see how to create your own plugins.

Installation

It is strongly recommended that you use a released version. Release binaries are available on the releases page. Follow the instructions to install Kubebuilder.

Getting Started

See the Getting Started documentation.

Quick Start

Also, ensure that you check out the Deploy Image Plugin. This plugin allows users to scaffold API/Controllers to deploy and manage an Operand (image) on the cluster following the guidelines and best practices. It abstracts the complexities of achieving this goal while allowing users to customize the generated code.

Documentation

Check out the Kubebuilder book.

Resources

Motivation

Building Kubernetes tools and APIs involves making a lot of decisions and writing a lot of boilerplate.

In order to facilitate easily building Kubernetes APIs and tools using the canonical approach, this framework provides a collection of Kubernetes development tools to minimize toil.

Kubebuilder attempts to facilitate the following developer workflow for building APIs

  1. Create a new project directory
  2. Create one or more resource APIs as CRDs and then add fields to the resources
  3. Implement reconcile loops in controllers and watch additional resources
  4. Test by running against a cluster (self-installs CRDs and starts controllers automatically)
  5. Update bootstrapped integration tests to test new fields and business logic
  6. Build and publish a container from the provided Dockerfile

Scope

Building APIs using CRDs, Controllers and Admission Webhooks.

Philosophy

See DESIGN.md for the guiding principles of the various Kubebuilder projects.

TL;DR:

Provide clean library abstractions with clear and well exampled godocs.

  • Prefer using go interfaces and libraries over relying on code generation
  • Prefer using code generation over 1 time init of stubs
  • Prefer 1 time init of stubs over forked and modified boilerplate
  • Never fork and modify boilerplate

Techniques

  • Provide higher level libraries on top of low level client libraries
    • Protect developers from breaking changes in low level libraries
    • Start minimal and provide progressive discovery of functionality
    • Provide sane defaults and allow users to override when they exist
  • Provide code generators to maintain common boilerplate that can't be addressed by interfaces
    • Driven off of //+ comments
  • Provide bootstrapping commands to initialize new packages

Versioning and Releasing

See VERSIONING.md.

Troubleshooting

  • Bugs and Feature Requests:

    If you have what looks like a bug, or you would like to make a feature request, please use the Github issue tracking system. Before you file an issue, please search existing issues to see if your issue is already covered.

  • Slack

    For realtime discussion, you can join the #kubebuilder slack channel. Slack requires registration, but the Kubernetes team is open invitation to anyone to register here. Feel free to come and ask any questions.

Contributing

Contributions are greatly appreciated. The maintainers actively manage the issues list, and try to highlight issues suitable for newcomers. The project follows the typical GitHub pull request model. See CONTRIBUTING.md for more details. Before starting any work, please either comment on an existing issue, or file a new one.

Supportability

Currently, Kubebuilder officially supports OSX and Linux platforms. So, if you are using a Windows OS you may find issues. Contributions towards supporting Windows are welcome.

Apple Silicon

Apple Silicon (darwin/arm64) is supported using the go/v4-alpha plugin which provides support for this platform.

kubebuilder init --domain my.domain --repo my.domain/guestbook --plugins=go/v4-alpha

Note: The go/v4-alpha plugin is an unstable version and can have breaking changes in future releases. The previous kustomize version (v3.Y.Z) used in the go/v3 has no available binaries for this platform kubernetes-sigs/kustomize/issues/4612 Because of this, we cannot support this darwin/arm64 on the stable scaffold done by default with the Kubebuilder with the go/v3 plugin.

Community Meetings

The following meetings happen biweekly:

  • Kubebuilder, Controller Runtime, and Controller Tools
  • Kubebuilder Triage

You are more than welcome to attend. For further info join to kubebuilder@googlegroups.com.